The invention relates to a device for ventilating a fuel tank.
Devices of the aforementioned type are provided in motor vehicles between the fuel tank and an activated carbon filter, which is intended to prevent an undesired release of volatile hydrocarbons from the fuel tank into the environment of the motor vehicle. The tank shut-off valve is a controllable valve, for example an electromagnetic valve which is normally closed and is opened during refueling of the fuel tank, to conduct a gas mixture which is displaced from the tank, through the activated carbon filter and to adsorb the hydrocarbons (HC) contained in the gas mixture, so that only purified air is released into the environment. The two tank pressure control valves are an overpressure valve and a negative pressure valve, which are also normally closed. The overpressure valve opens automatically, when a predetermined overpressure is established inside the fuel tank as a result of evaporation of fuel inside the fuel tank, for example when ambient temperatures rise or during a residual heating period after turning off the internal combustion engine, while the negative pressure valve opens automatically when a predetermined negative pressure is established inside the fuel tank as a result of fuel condensing inside the fuel tank, for example when ambient temperatures fall.
Known devices of this type are usually configured as valve unit or valve assembly, in which the tank shut-off valve and the two tank pressure control valves which are configured as bypass valves are combined. Depending on the configuration, these valve units are mostly constructed so that a tank connection, which communicates with the fuel tank and a filter connection of the valve unit which communicates with the activated carbon filter point in different directions or project in different directions over the valve unit, respectively. This ensures an optimal draining of condensate in only one mounting position of the valve unit, while in other mounting positions so called dead fuel regions can occur from which the fuel can no longer drain. When the condensate contains moisture, this can lead to a freezing in the case of low ambient temperatures and especially in the tank shut-off valve can lead to damage to or destruction of the valve.